I'm rebuilding a 1929 350cc L-29 Sloper. Most of it is back together but I have a concern about the big end oil feed. There is a bronze bush in the timing cover that fits over a threaded shaft/stud on the end of the crankshaft. The bush is fed with oil direct from the oil pump.

My concern is whether there is something needed to improve the seal between the bush and the threaded shaft to minimise oil leakage? I've made a felt oil seal that bears against the end of the bush but I'm not sure if this is part of the original design. The end of the shaft has a small indentation and I wonder if there is some sort of jet intended to fit in here - maybe something spring loaded that fits within the bush. I've scoured the parts manuals and can't find anything that I'm missing from my engine. If anyone on here knows for sure how this seal is made I'd be very grateful for a reply as it may set my mind at rest about the nature of the oil feed.

Here are some pics showing the stud/shaft, the bronze bush in the timing cover and my attempt at a felt seal:

The gear on the shaft just looks like an idler gear to me. Are you sure the shaft actually turns? Or are you just trying to seal the gap between the nut and the bushing to keep oil from leaking into the cavity?

The shaft definitely turns - the threaded portion is for the nut that holds the crankshaft timing gear in place. It's a running fit in the bronze bush. You can see in the pic that the thread form itself is flattened off where the shaft fits within the bush but the interior of the bush is not scored, so I don't think this flattening is due to wear, I think it is how it was designed and made. I don't think it is a repair or bodge of any sort. I take your point though about the felt probably not lasting long on the thread.

Here's a picture from the 1929 catalogue showing a cross-section of the Sloper engine. The bit I'm asking about is labelled 'K'. There's no felt seal visible in this picture but it isn't an engineering drawing, hence my question to anyone who has first-hand knowledge of this engine.

The shaft threads for the nut were stripped, so Mr Bodger cut a smaller diameter thread all the way along it.

Look for another crankpin or whole crank assembly to buy, or investigate getting the pin removed, built up and re-machined.

Thanks! At least I know now what it should be like, although it looks like a major job to fix the problem. The 350cc engine that I have has a different stroke to the 500, so a replacement 500 crank won't work - I'd need barrel and head too.

The mainshafts are pressed into the flywheels & riveted in place. There is a flange on the inside.I had a new drive side mainshaft made for my 1935 BSA W35/7.You have to buy quite a large diameter piece of EN36B because of the diameter of the inboard flange.The flange was something like 2 " in diameter , shaft 3/4 " if I remember correctly.I machined it roughly to size on the Colchester Student lathe at work & then took it to a retired tool & die maker to finish it off.

And a slightly different variation on the same theme.Make up a sleeve nut to fit over the threaded section with an Id to run in the bush.If you have access to a lathe easy job provided ther will be sifficient wall thickness.

That looks to be a good idea. I need to accurately check the OD of the shaft and the ID of the bush. If they're a close match then I'll probably leave it as is - I believe the engine has been running in the past with this bodge. The shaft runs inside the bush for a fair distance so if the diameters are close then I don't think that much oil will be lost down the shallow thread instead of passing into the crankshaft.

The oil feed is adjustable, and the manuals refer to setting the pump so that a puff of blue smoke is seen when the throttle is opened. This should give me some leeway too. I've got a 1930 250cc BSA with the same arrangement as the Sloper so I have a bit of experience with the oiling system.

Seems you're determined to stick to the bodge to avoid pulling it apart.

Yup. The engine has been running with this bodge. I will ride it perhaps 400 miles per year max. If it fails (and I don't believe it will) I'll fix it then. In the meantime I'll be riding the bike, rather than having it strewn in bits for another xx months or years. I also use as many of the original fasteners and other components as I possibly can. I could replace old slightly chewed fasteners with new stainless ones - but this bike is 85 years old and I want it to look that way. Same applies to this bodge - it's part of the history of the bike.

I would fix it but as its a roller bearing big end it needs no oil pressure just a small flow of oil so that should not be affected, its the piston that is more likely to suffer from lack of oil splash from the big end.

You can accidentally leave out the oil pump seal on a Norton oil pump, as long as the pump floods the entry to the crank then the centripetal force from the oil at the big end will drag oil through the crank and give a supply enough for the engine not to seize in the short term. This is a similar situation and the engine will survive in the short term but its not something you plan to do and needs fixing ASAP.

I use a leather seal on my sloper, having remade that bronze bush to be a snug free-running fit. But I agree with you.. yours will probably run perfectly fine as is, even with that thread on the quill. (At least the spiral tends to push the oil back in to the bush eh!)I attach a photo of the bsa assembly drawing which shows the seal.

with the original felt seal that i removed from the engine when I rebuilt it, or my leather seal, I found the seal snags on the timing gear nut and so spins with the crank and polishes the concave bush, rather than becoming shredded. After around 1500 miles the oil pressure on my tank-mounted gauge drops from 3 to 1 PSI as the seal eases off. But after 4000 miles i had good compression but rebuilt with a high compression piston & barrel and new seal on the crank anyway. All was still otherwise good at 4000 miles including the bore and the new Alpha big end.

I know the oil gets to the bore from that blue haze that the handbook describes. I have my oil knob open just 3 flats (1/2 turn from fully shut). It took me quite a while to find the confidence to turn it that low... But I have undertaken regular long motorway journeys with full camping gear like this (e.g 2014 John Bull, BSAOC Summercamp in Belgium etc).

I think the only downside maybe something I experienced when first running in with the knob open 3-5 turns, i.e the timing side will tend to fill more than it need do, So oil can get past the cam followers and even fill the push rod tubes (I sealed my telescopic push rod tubes with leather seals only to have the oil then rise to the rocker box!).. If you don't have a felt seal in the taper behind the Magneto timing gear, it might exit also between Timing chest and Mag... However... just closing down the oil supply solved all that.

I use Morris Golden Film SAE 40 mostly. It revs more freely than SAE50 but using SAE50 on the 400 mile summercamp trip I only used 1.5 litres of oil. These bikes original pistons have no Oil ring of course, and there is no engine breathing, so I was quite pleased at that.